Development of a Probabilistic Tsunami Hazard Analysis in Japan

Abstract

It is meaningful for tsunami assessment to evaluate phenomena beyond the design basis as well as seismic design. Because once we set the design basis tsunami height, we still have possibilities tsunami height may exceeds the determined design tsunami height due to uncertainties regarding the tsunami phenomena. Probabilistic tsunami risk assessment consists of estimating for tsunami hazard and fragility of structures and executing system analysis. In this report, we apply a method for probabilistic tsunami hazard analysis (PTHA). We introduce a logic tree approach to estimate tsunami hazard curves (relationships between tsunami height and probability of excess) and present an example for Japan. Examples of tsunami hazard curves are illustrated, and uncertainty in the tsunami hazard is displayed by 5-, 16-, 50-, 84- and 95-percentile and mean hazard curves. The result of PTHA will be used for quantitative assessment of the tsunami risk for important facilities located on coastal area. Tsunami hazard curves are the reasonable input data for structures and system analysis. However the evaluation method for estimating fragility of structures and the procedure of system analysis is now being developed.

Stochastic analysis and uncertainty assessment of tsunami wave height using a random source parameter model that targets a Tohoku-type earthquake fault

“…Thus, although there are some differences in the conditions of the studies, we discuss the results of the analyses in the following. In the long-term averaged hazard curve of Sakai et al (2006), wave heights with a return period of 1,000 years had a range of about 3.5 m (0.05 fractile wave) to about 5.6 m (0.95 fractile wave). However, in our study, wave heights with a similar return period had a range of about 4.0 m (0.05 fractile wave) to about 17.3 m (0.95 fractile wave).…”

“…3.1 with the observation results of the Tohoku earthquake that occurred in 2011 and a past study performed by Sakai et al (2006). The measurement data of the south Iwate offshore GPS wave gauge and the Fukushima Prefecture offshore GPS wave gauge set up by MLIT and analyzed by Port and Airport Research Institute (PARI) were used as the Tohoku earthquake observation data ).…”

“…According to our analysis, the return period of the Tohoku earthquake of approximately 600 years is equivalent to a fractile between 0.35 and 0.75; this is a relatively wide fractile range. Sakai et al (2006) also conducted probabilistic tsunami hazard analysis using the logic-tree approach, targeting the coast of Fukushima Prefecture. Before comparing our research with their work, it is important to note that one of the fundamental differences between the two studies is that our research considers only the Tohoku earthquake type fault (M w 8.9-9.1), while their research considered nine earthquake faults (M w 7.7-8.6) along the Japan trench for the near-field tsunami.…”

Insights on Accident Information and System Operations during Fukushima Events

“…In Fukushima Daiichi NPPs, the design basis for flooding by tsunamis was originally 3.1 m at the time of the construction permit, with this later reevaluated to 5.7 m based on the methodology proposed in 2002 [20]. Based on a recognition that tsunami heights may exceed the design basis, Sakai et al [21] performed probabilistic tsunami hazard analysis in 2006, estimating the frequency of tsunamis higher than 15 meters in 50 years to be approximately four occurrences in every 100,000 years.…”

Sustainable, Full-Scope Nuclear Fission Energy at Planetary Scale

“…For example, such a service could have revealed the relatively severe susceptibility of the Fukushima Daiichi nuclear power station to tsunamis, which had been known prior to the 2011 Tohoku Earthquake [18,19] but which facts were not disseminated to degrees sufficient to politically compel corrective actions. Possible issues of intrusiveness into 'internal affairs' of utilities and owner-nations were settled rather definitively in the aftermath of the Chernobyl catastrophe, as nations sharing the Eurasian continent and its airspace demanded, oversaw and co-sponsored the safety upgradings or retirements of nuclear power reactors that shared the shortcomings of the Chernobyl design.…”